Hepatitis B virus (HBV) is an agent which infects man, integrates into the genome of a specific tissue (liver), and probably causes hepatocellular carcinoma (HCC). In the United States, there are over three quarters of a million individuals with persistent HBV infection and worldwide, HCC is one of the leading causes of death from cancer. The purpose of this proposal is to study the strategies and molecular mechanisms utilized by the hepatitis B virus (HBV) to understand its hepatotropism, genetic regulation, and association with pathologic conditions especially its role in liver carcinogenesis. Our underlying hypothesis is that the HBV genome has evolved mechanisms of gene regulation and expression similar to those utilized by host genes as an adaptation for an efficient symbiotic relationship with its host. Mouse embryo microinjection technology has been used to construct an animal model simulating the chronic carrier state. Such HBV transgenic mice, in which the newly acquired HBV genome is expressed and transmitted in kindreds of mice will allow the genetic dissection of HBV gene expression, regulation, and function. This system appears ideally suited to examine the influence of host genes on HBV expression, the developmental regulation of HBV sequences, and the associated factors potentially linking HBV to the multistep process of hepatocarcinogenesis. In addition, the viral genetic requirements for tissue specific expression will be examined in liver cells in vivo. Such an approach has broad applicability towards elucidating novel mechanisms of higher eukaryotic gene expression and regulation. Our program involves the isolation and characterization of nucleic acids by Southern blot analysis, Northern blot analysis, primer extension, cloning, and sequencing. Viral proteins will be identified and studied using monoclonal antibodies by immunohistochemistry and protein blotting. Hepatocarcinogenesis studies will examine the relationship of treating HBV transgenic mice with such agents as aflatoxin B1 and alcohol upon the development of liver pathology and the incidence of liver tumors in such mice followed over time.